HIV incidence and mortality decreased globally, yet increased markedly in the Commonwealth of Independent States (CIS) of Eastern Europe and Central Asia where HIV epidemics remain volatile and fueled primarily by people who inject drugs (PWIDs) with opioid use disorders (OUDs). Regional drug policies favoring incarceration have resulted in 5 CIS countries being among the 10 countries with the highest rate of incarceration. In this region, HIV is concentrated 18- to 50-fold higher than in communities. Data from multiple settings where PWIDs and people living with HIV (PLH) are concentrated (i.e., prisons) reveal that such structured settings can be effective sites for HIV prevention. In the absence of preventive evidence-based interventions (EBIs), prisoners often engage in risky HIV behaviors both within prison and post-release. One of the most effective HIV prevention EBI is opioid substitution therapy (OST), but this EBI is mostly absent from or markedly under-scaled in CIS prisons. We have successfully completed and exceeded our original 3 aims. First, we created a new research collaboration called PRIDE (Prison-related Research, Intervention Development and Evaluation), which focuses on integrating research and policy with Prison Departments and local and international stakeholders in CIS countries. Second, we exceeded the number of biosurveillance prison surveys conducted and established a new method that is now endorsed by CDC, WHO and UNODC. We documented the extraordinary burden of HIV, other infectious diseases and substance use disorders, and community-transition challenges and recorded the highest recorded rate of within-prison drug injection among HIV+ prisoners. Third, we uncovered markedly negative attitudes toward OST, PWIDs and PLH among prison personnel, which was mediated by provision of accurate knowledge and could be improved using a brief intervention that we adapted from social marketing and decision science strategies. Fourth, we assisted with introducing pilot OST programs in two CIS countries. Last, because none of the countries had transitional care programs, including the ones where we introduced OST, we began the process of developing a MATLINK protocol (linkage to OST), that is based on another EBI - SBIRT (screening, brief intervention and referral to treatment). Findings presented to local and PRIDE stakeholders resulted in the request by several member countries to focus on either introducing or expanding OST within prisons, an EBI, or where local laws, policy or cultures were uncommitted, all PRIDE stakeholders stated their commitment to linking prisoners to OST post-release. This renewal application builds on our existing implementation science framework where we propose a series of related activities that involve improving access to OST either within prison and/or linking them to it post-release. Our three related specific aims involve creating and pilot testing culturally congruent MATLINK protocols within partner countries, assessing organizational barriers to MATLINK and intervening with prison staff, and using a multi-level implementation science framework, assessing client-level outcomes for the MATLINK protocol in each setting. Our productive team consists of international researchers and collaborating sites with demonstrated successes working in the political and legal context in CIS countries and prisons. Our collective research experience includes implementation science, criminal justice settings, introducing and expanding OST, EBIs, and HIV prevention.